Vehicles that are adapted to carry load material may eject the material by raising the front end of the load area so that the material slides down the load area off the rear of the vehicle. However, raising the load area raises the centre of gravity of the vehicle and therefore reduces the stability of the vehicle so that ejection of the material whilst the vehicle is moving, particularly when moving on inclines, side slopes or soft ground, may not safely be achieved.
Alternatively, the material may be ejected from the vehicle using an ejector blade that moves along the bed of the load area from the front to the rear, pushing material out of the rear of the vehicle. Because the centre of gravity of the vehicle is not raised by the operation of the ejector mechanism, it may be possible to eject the material whilst the vehicle is moving. This may be particularly useful where the material needs to be spread across the ground along which the vehicle is travelling, for example in road building operations. By spreading the material at the time of ejecting it from the vehicle, the subsequent need for material spreading apparatus, such as bulldozers, may be reduced allowing for faster cycle times and reduced costs.
US 2004/0173088 describes a vehicle with an ejector blade that moves along the bed of the load area in order to eject material from the rear of the vehicle. The ejector blade is driven by a hydraulic multistage cylinder, wherein each cylinder has a different fluid volume. The vehicle is arranged such that an operator inputs a desired ejector blade speed and a control system ensures that that chosen ejector blade speed is maintained, regardless of the cylinder that is currently driving the ejector blade. If the vehicle operator maintains a constant vehicle speed, the ejected material may be spread evenly on the ground. However, this requires the operator to control the vehicle speed carefully, which increases the difficulty of vehicle operation. Furthermore, when the vehicle operator is unable to maintain the vehicle speed, for example because an obstruction necessitates a reduction in speed, or an incline results in a reduction in speed, the material may no longer be spread evenly.